The present invention relates to a novel resin-preimpregnated, textile material which can in particular be used in the production of laminated articles or various coatings.
Laminated articles based on thermosetting or thermoplastic resin reinforced by a textile insert have long been known and are used for many different purposes in various fields.
In general, such articles are made by impregnating a textile reinforcing material, such as a fabric, felt, sheet of threads or the like. Optionally, the textile reinforcement can be obtained by superimposing several layers of the same or different types which may or may not be crossed, as a function of the mechanical characteristics which it is intended to give to the material.
Impregnation is preferably carried out by means of a thermosetting resin such as a phenol resin, epoxy resin or polyester resin, which is polymerised under the action of heat and/or pressure.
Moreover, for certain applications in which it is desired to obtain materials with a particularly high strength in all directions, and particularly a resistance to splitting off, it has been proposed to use as the textile reinforcing element three-dimensional articles, i.e. having threads in all three directions. Thus, it has been proposed to superimpose layers of longitudinal and transverse threads and to interconnect said layers by seams permitting the introduction of threads in the thickness direction of the article.
Other equivalent methods make it possible to obtain similar articles.
In general, threads which are not resin-impregnated and often called "dry threads" are used in the production of this type of textile reinforcing articles, impregnation taking place once the textile article is finished.
However, during the production of laminated articles, with a dense textile insert and/or a large thickness it is virtually impossible to obtain a homogeneous distribution of the resin up to the core of the material. This structural heterogeneity of the material leads to numerous problems such as irregular mechanical properties and the danger of splitting off when the material is in the form of several layers.
To solve this problem, and obtain a good impregnation by the resin, it has been proposed to use resin-preimpregnated textile sheets or threads. This preimpregnation can either be carried out beforehand on the thread which is to be used in the formation of the textile sheet, or by impregnating the sheet after its formation from the dry threads.
When it is desired to produce resin-impregnated threads comprising a plurality of substantially parallel filaments, impregnation is generally obtained by passing these threads througha resin bath and calibrating by means of a spinneret. These preimpregnated threads are used to make laminated materials in which layers of parallel threads are formed. The layers are optionally crossed relative to one another and the resin is polymerised after forming the layers.
This procedure makes it possible to produce articles in which the resin distribution is homogeneous, but it has been found that for certain applications, in which the laminated materials are subject to high stresses and loads, there is still a risk of splitting off between the various layers.
Moveover, it is relatively difficult to store such resin-preimpregnated threads and it is generally necessary when they are stored in the form of a coil to provide a separating element between each layer of turns, for example a sheet of siliconed paper which prevents sticking between the individual layers. Moreover, in this case, the coil cannot be formed from contiguous turns, which limits the quantity of material which can be stored on each coil.
Furthermore, due to their adhesive properties, it is not possible to partly or wholly used such preimpregnated threads for the production of conventional warp and weft fabrics and for the production of three-dimensional textile articles.
Finally, the thus preimpregnated threads are either in the form of a flat wick of limited thickness in which the filaments are parallel to one another or in the form of a substantially elliptical member, but it has been found that it is virtually impossible to obtain a thread with a strictly circular cross-section, which is particularly advantageous when making high density materials.
In addition, the cross-sectional shape of the threads produced in this way can be deformed of modified during subsequent manipulations, making numerous precautions necessary during the latter.
It has also been proposed to make partly polymerised resin-preimpregnated textile materials in order to eliminate the adhesive properties. These materials are either in the form of filiform elements or in the form of sheets of limited thickness. They have a certain rigidity, which facilitates their storage and optionally their use for certain special applications, for example when it is desired to produce articles having a complex shape in which it is necessary to cut the material either to a precise shape in the case of a sheet, or to a given length in the case of a filiform element.
In both cases, the thus produced resin-preimpregnated textile material has a substantially smooth outer surface and the resistance to splitting off between the different layers formed is limited then due to this surface state.